1. Field of the Invention
The present invention generally relates to methods for forming lithium alloys through kinetically controlled lithiation, and more particularly to a technique which simplifies lithium alloy fabrication and the control of alloy morphology through deposition on a temperature regulated substrate.
2. Discussion of the Related Art
A diversity of methods are known for combining materials in the fabrication of alloys or other devices. One of these, molecular beam epitaxy (MBE) is a process that has been applied to the fabrication of magnesium-lithium alloys. However, as is known, molecular beam epitaxy has certain shortcomings, including difficulty in implementation, expense, and time. Molecular beam epitaxy offers a means to control relatively complex fabrication processes but it is subject to rather rigid constraints (when performed properly). As a result, it is a rather expensive process to implement. In addition, growing epitaxial layers through this process is an extremely slow process. When used to combine elements such as magnesium and lithium, the MBE technique maintains relatively low concentration levels so that the magnesium and lithium constituents do not interfere with each other during the depositions process and can be combined on an appropriate substrate.
To date, there is some use of magnesium-lithium alloys in the automotive industry, and there have been suggestions of its possible use in battery technology. The rapid and controlled creation of this alloy and, especially the control of its morphology has offered a challenge to current technology. In some part, this results from the relatively high vaporization temperature of magnesium. Due to its magnesium-oxide (MgO) outer coating, it has been found that a magnesium ingot may be heated to 700 degrees C. and still remain intact.
A shortcoming of the prior art relates to the cycle life of lithium electrode batteries. It has been found that, during lithium battery recharge, the return of lithium ions to the negative battery electrode can lead to dendrite formation. This dendrite formation is believed to be the result of the inability of lithium to diffuse readily into the surface of a lithium electrode. Because of this slow diffusion into the electrode surface and bulk, the deposited lithium can grow out from the electrode as dendrites form. As the battery cycles (discharges/recharges) over time, the dendrite formation continues until one or more dendrites creates a short within an interior cell of the battery. This situation has been addressed with the creation of lithium ion batteries, however, at lessor rate capabilities and energy densities.
In prior art applications, aluminum-lithium alloys are well known. For example, the fuel tanks of the space shuttle use, or intend to use, an aluminum-lithium alloy. This alloy provides a lighter weight alternative, therefore requiring less fuel consumption. It is desirable to reuse these tanks. However, this may be problematic due to the surface heat generated upon re-entry into the earth's atmosphere. As the tanks heat up, lithium can leach out of the aluminum. Accordingly, a technique which can potentially be used to replace the lithium lost to the surface of this and other aluminum-lithium alloys is needed.
With its light weight and optimal diffusivity, lithium incorporation can offer the potential for a wide range of improvements which include the development of new compact battery electrodes, the fabrication of new lower density alloys for the aerospace and automotive industries, the development of new selective catalysts for the oxidative coupling of methane to form C.sub.2+ hydrocarbons, and the creation of pinning sites in superconductors.
Accordingly, it is desirable to develop new alloy forming techniques and means to incorporate lithium using approaches which address these and other shortcomings in the prior art.